The feeding strategies of the antarctic lanternfish electrona antarctica (pisces: myctophidae) in the amundsen and cosmonaut seas (southern ocean), assessed with a classification tree analysis

Myctophid fishes represent an important trophic link between zooplankton and higher trophic level predators in the oceanic ecosystems of the Southern Ocean. The Antarctic lanternfish (Electrona antarctica) is one of the most abundant myctophids in the Southern Ocean; however, information on their feeding habits is sparse, representing a key area of uncertainty in efforts to model Southern Ocean food web dynamics. Using a classification tree approach based on stomach content data, we explored the feeding strategy of E. antarctica in the Amundsen and Cosmonaut Seas during January and March 2021, as well as its variation in relation to ontogenetic stage and sampling area. An ontogenetic shift in the feeding preference of E. antarctica was identified in the Cosmonaut Sea: Fish smaller than 48 mm fed on ostracods and copepods, while larger fish (SL > 62 mm) relied primarily on krill. Conversely, there was no ontogenetic shift in the diet of E. antarctica in the Amundsen Sea, and this species feeds almost exclusively on Themisto gaudichaudii. The diet composition of E. antarctica presented spatial differences: Copepods (48% IRI) and krill (24% IRI) were consumed more in the Cosmonaut Sea, while amphipods (91% IRI) were consumed more in the Amundsen Sea. The spatial differences in the prey of E. antarctica are related to the oceanographic environment and the variety of plankton prey in different regions. We determined that the size of E. antarctica, sea surface temperature (SST), latitude, and chlorophyll-a concentration (Chl) were the most important variables associated with dietary differences. When the fish size is larger than 55 mm and the krill abundance is high, E. antarctica mainly preys on krill. Since E. antarctica occupies a key position in the mesopelagic fish community, increased knowledge of the trophic ecology of this fish would contribute to a comprehensive understanding of its response to environmental changes.